Highly accelerated EPI with wave encoding and multi-shot simultaneous multislice imaging.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Neuroimaging

Background:

• Echo Planar Imaging (EPI) is crucial for fast MRI acquisition but suffers from artifacts and g-factor penalties at high acceleration rates.
• Existing acceleration techniques often struggle to balance speed with image quality, limiting applications in diffusion and functional imaging.

Purpose of the Study:

• To introduce Wave-EPI, a novel acquisition and reconstruction technique for highly accelerated EPI.
• To reduce the g-factor penalty and image artifacts commonly associated with accelerated EPI.

Main Methods:

• Wave-EPI employs sinusoidal gradients during EPI readout to spread aliasing, optimizing the use of 3D coil sensitivity profiles.
• A
• half-cycle
• sinusoidal gradient is proposed to increase voxel spreading within slew rate and nerve stimulation constraints.
• Multi-shot Wave-EPI minimizes distortion and blurring at high resolutions, with structured low-rank regularization addressing shot-to-shot phase variations.
• Gradient imperfections are managed using polarity-specific point spread functions calibrated via a FLEET-based scan.

Main Results:

• Wave-EPI successfully enabled whole-brain single-shot gradient-echo and multi-shot spin-echo EPI acquisitions at high acceleration factors (R_in × R_sms = 3 × 3) at 3T.
• Combined with g-Slider encoding, Wave-EPI improved signal-to-noise ratio in 1 mm isotropic diffusion imaging.
• Compared to blipped-CAIPI, Wave-EPI achieved up to 1.21-fold and 1.37-fold reductions in average and maximum g-factors, respectively.

Conclusions:

• Wave-EPI offers a method for highly accelerated single- and multi-shot EPI with significantly reduced g-factor and artifacts.
• This technique holds promise for advancing clinical and neuroscientific applications by enhancing spatial and temporal resolution in functional and diffusion MRI.